Highly loaded cast polyurethane propellants containing aluminum

ABSTRACT

A CASTABLE SOLID ROCKET PROPALLENT HAVING INCREASED SOLIDS-TO-BINDER RATIO FOR USE IN VOLUME LIMITED MISSILE SYSTEMS.

U t d tates Pate t l c Navy No Drawing. Filed Oct. 20, 1966, Ser. No. 588,692

Int. Cl. C06d /06 US. Cl. 149-194 f 2 Claims ABSTRACT or run DISCLOSURE:

A castable solid rocket propellant having increased solids-to-binder ratio for use in volume limited missile systems.

This invention relates to castable solid rocket propellants having increased solids-to-binder ratio and to the preparation thereof.

Composite solids rocket propellant grains normally consist of one or more solid inorganic or organic oxidizers uniformly distributed through a matrix of a fuel-binder material. In addition, the propellant may contain liquid and solid additives to enhance the ballistic and physical performance of the rocket. Highly loaded solid propellants are of interest for both high impulse and high density. The present invention provides propellant grains prepared from concentrated slurries of polar solids and relatively little nonpolar liquids.

It is therefore an object of the present invention to provide solid propellant grains with high solids loadings which will yield higher boost velocities when used in volume limited missile systems than have been obtained heretofore.

Another object is to provide a basic technique of formu- I U lation which can be applied to the filling of other polymer systems with a high volume percent of solid particles.

Other objects, features and many of the attendant advantages of this invention will become readily appreciated as the same become better understood by reference to the following detailed description.

The invention consists of castable polyurethane compositions containing aluminum and ammonium perchlorate with very high volume loadings of solid particles. These propellants were prepared by the use of selected wetting agents and binder compositions in conjunction with spheroidal solid particles in optimum particle size distributions. In general the propellant prepared by using the selected wetting agents have volume loading ranging from 75 to 81.7 volume percent with densities ranging from 1.8 to 1.9 g./ cc. at 25 C. The binders are of the polyurethane type prepared with various polymeric diols and tn'ols and mixtures thereof with both aliphatic and aromatic diisocyanates. Plasticizer contents range from 40 to 60 weight percent based on total binder weight, and are composed of organic compounds containing nitro groups, compounds without nitro groups or both. A propellant with excellent mechanical properties is obtained with diol to triol equivalent weight ratios in the polyurethane binder varying from 80:20 to 20:80, depending on the relative molecular weights of the prepolymers. The diisocyanate equivalent weight ratios are held between 107 and 110. Catalyst levels, ferric acetonylacetonate, range between 0.02 weight percent and 0.08 weight percent depending on the binder composition.

3,811,957 Patented May 21, 1974 The wetting agent used herein was adiponitrile. Others were found comparable.

A typical propellant formulation containing 90 percent by weight (81.7 volume percent) total solids is as follows:

Ingredients: Percent by weight Solids: I

7 Aluminum, 31p. 17.50 fuel.

Aluminum, 1. 7.50 fuel.

Ammonium perchlorate, 450,41. 45.50 oxidizer. Ammonium perchlorate, 150 1. 13.00 oxidizer. Ammonium perchlorate, 25y. 6.50'oxidizer.

- Binder:

Adiponitrile 0.20 wetting agent. Ferric acetonylacetonate 0.02 catalyst. Bis-2,2-dinitropropylacetal 3.00 plasticizer. isodecyl pelargonate 1.02 plasticizer. v

. Prepolymer of 1,2,6-hexametriol and polypylenc Y oxide 4.66 plasticizer. Neopentylglycol a z e l a t e polyester z 0.68 plasticizer.

0.02 crosslinker. 0.40 crosslinking agent.

This propellant has a density of 0.0692 lb./in. and a measured specific impulse in 100-lb. motor of 243.6 lbf.- sec./lbm."at 1000 p.s.i.a. expanded to 14.7 p.s.i.a with a 15 cone angle. It has an elongation at 25 C. of over 20% and a tensile strength of 60 to 100 p.s.i.

Various blends of aluminum and ammonium perchlorate have been used depending on the solids loading desired ranging up to weight percent.

Wetting agents found to be comparable to adiponitrile were bis- 2-cyanoethyl, bis-Z-cyanoethyl sulfide, and bis-2- cyanoethyl methyl amine. They give comparable results. A casting slurry could not be obtained at the high solids loading with other wetting agents. Up to 0.2 weight percent of wetting agent was found to have no effect upon the mechanical properties. Quantities greater than 0.2 weight percent tended to decrease tensile strength and increase elongations of the resulting propellant. In other applications the optimum levels of these wetting agents will vary depending on the nature of the surface to be wetted, the total quantity of solids used, and the termminal functional groups of the wetting agents.

Other plasticizers are dioctyl azelate, octyl diphenyl phosphate and bis-2,2-dinitropropyl formal.

Typical diols which may be useful are polyoxybutylene glycol, disebacate of polyoxybutylene glycol, and tripropylene glycol azelate polyester.

Hexamethylene diisocyanate and 2-nitrazapentane diisocyanate were used in the place of 2,4toluene diisocyanate with excellent results.

The disebacate of polyoxybutylene glycol, ferric acetonylacetonate, bis-2,2-dinitropropyl acetal, isodecyl pelargonate, neopentyl glycol, azelate polyester, triethanol amine and 2,4-toluene diisocyanate were mixed in a sigma blade mixer. Several othertypes mixers can also be used. The ammonium perchlorate of varying size which had been dry blended was added and the mixing continued for about 15 minutes. At this point the aluminum powder which had been previously mixed together was added. The temperature was increased from room temperature to about 40 C. and mixing continued for about 30 Triethanol amine 2,4-toluene diisocyanate motors and cured for about48 hours attemperatures ranging from 75 to 80 C.

Many binder variations are possible with the wetting agents herein disclosed. The high-impulse, high-density, high-volume-loaded propellants possible with the formulations of the invention extend the usefulness of polyurethane propellants. The wetting agents used herein are short chained aliphatic molecules terminated at both ends by polar functional groups. Common wetting agents such as lecithin are bulky molecules with their polar groupings concentrated at one end of the molecule and tend to form a thick absorbed layer. The wetting agents used in this invention are short chained aliphatic molecules terminated at both ends by polar functional groups as wetting agents. Such structures minimize the thickness of the absorbed layer. Functional groups at each end cause the molecule to lie fiat on the solid particle surface. The chain length between functional groups should be short to prevent coiling of the chain. Coiling will increase the thickness of the absorbed layer. In considering the physical structure of a model propellant slurry composed of spheres of uniform size in a liquid medium, the thickness of the adhered layer is important. Such an absorbed layer acts to increase the effective solid particle size (diameter) by twice the thickness of the adhered layer. Since the volume percent void space in such a system is independent of the diameter of the spheres, the actual volume of void spaces, and the corresponding liquid volume necessary to fill them is increased in direct relation to the thickness of the absorbed layer. For these reasons, the minimum volume of liquids necessary to form a castable slurry with a given volume of solid particles is dependent on the thickness of the absorbed layer as well as the surface area of the particles and their size distribution.

Obviously many modifictions and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A solid propellant composition comprising the following Percent by weight Ingredients:

Solids 75 to 90 Binder to 25 said solids consisting essentially of an inorganic oxidizer and-a-metal powdemand 7 said binder comprising a polyurethane type consisting essentially of dials and triols and mixtures thereof, both aliphatic and aromatic diisocyanates, a plasticizer composed of organic compounds containing nitro groups, a catalyst and a wetting agent; said wetting agent selected from the group consisting of adiponitrile, fi, 3'-dicanodiethyl sulfide, fi,,3'-dicanodiethyl ether, and fl,;3'-dicanodiethyl methyl amine. 2. A solid I propellant composition comprising the following:

said wetting agent being a member selected from the group consisting of adiponitrile, p,,3-dicanodiethyl sulfide, fi,/3'-dicanodiethyl ether and ,B,fl-dicanodiethyl methyl amine.

References Cited 1 UNITED STATES PATENTS 7/1962 Hass 149-19 3,092,527 6/1963 Schaafsma 149-19 3,132,976 5/1964 Klager et al. 149-19 3,141,294 7/1964 Lawrence et al. 149-19 3,215,573 11/1965 Winkler 149-19 3,245,849 4/1966 Klager et al. 149-19 BENJAMIN R. PADGETT, Primary Examiner U.S. c1. X.R. 149-20, 21, 1'13, 114 

